The present invention relates to a control of a system, machine or process that is repetitive in nature or is amenable to at least some degree of rehearsal. More particularly, the present invention relates to generating drive signals as input to a vibration system.
Vibration systems that are capable of simulating loads and/or motions applied to test specimens are generally known. Vibration systems are widely used for performance evaluation, durability tests, and various other purposes as they are highly effective in the development of products. For instance, it is quite common in the development of automobiles, motorcycles, or the like, to subject the vehicle or a substructure thereof to a laboratory environment that simulates operating conditions such as a road or test track. Physical simulation in the laboratory involves a well-known method of data acquisition and analysis in order to develop drive signals that can be applied to the vibration system to reproduce the operating environment. This method includes instrumenting the vehicle with transducers “remote” to the physical inputs of the operating environment. Common remote transducers include, but are not limited to, strain gauges, accelerometers, and displacement sensors, which implicitly define the operating environment of interest. The vehicle is then driven in the same operating environment, while remote transducer responses (internal loads and/or motions) are recorded as a record. During simulation with the vehicle mounted to the vibration system, actuators of the vibration system are driven so as to reproduce the recorded remote transducer responses (i.e. the record) on the vehicle in the laboratory.
However, before simulated testing can occur, the relationship between the input drive signals to the vibration system and the responses of the remote transducers must be characterized in the laboratory. Typically, this “system identification” procedure involves obtaining a respective model or transfer function of the complete physical system (e.g. vibration system, test specimen, and remote transducers) hereinafter referred to as the “physical system”; calculating an inverse model or transfer function of the same; and using the inverse model or transfer function to iteratively obtain suitable drive signals for the vibration system to obtain substantially the same response from the remote transducers on the test specimen in the laboratory situation as was found in the operating environment. (As those skilled in the art would appreciate, this process of obtaining suitable drive signals is not altered when the remote transducers are not physically remote from the test system inputs, for example, the case where “remote” transducers are the feedback variables, such as force or motion, of the vibration system controller.)
The inverse model is then used during simulation to obtain drive signals for control of the vibration system. However, depending on the desired simulation, it may be better to obtain and use a multiple region inverse model rather than a single inverse model. For example, under time history control, different inverse models would be used for different regions of a desired time history input. Typically, this involves using different inverse models in the control algorithm for different regions of the time history. However, implementing different inverse models successively in the control algorithm can cause instabilities and other unintended effects, which can cause damage to the vibration system or test specimen. Accordingly, improvements are needed to address these problems.